its jaws widely and apparently gulped in a large volume of air. It then descended and remained quiet for the usual interval.
Fig. 5.—View from below of the Upper or Dorsal Wall of the Throat of the Long-nosed Gar (Lepidosteus osseus). One-half Natural Diameter.
The œsophagus is removed excepting that part of the dorsal wall (Al) which is closely attached to the air-bladder (A). Its cut edges are indicated by x x. Ch is the opening or "chink" leading into the air-bladder, and C C indicate projecting points at the sides of the chink. HP, hypopharyngeal bones armed with teeth.
The escaping air should be chemically examined. But, so far as the experiments go, it seems probable that, with both Amia and Lepldosteus, there occurs an inhalation as well as exhalation of air at pretty regular intervals, the whole process resembling that of the Menobranchus and other salamanders, and the tadpoles, which, as the gills shrink and the lungs increase, come more frequently to the surface for air.
But the reader may say: "These fishes have gills, of course; but have they also lungs?" To this the answer is both yes and no; for there are at least two different ways of interpreting certain facts; and some definitions are not as yet wholly agreed upon.
Fig. 6.—Cross-Section of the Air-Bladder of L osseus. One-half Natural Diameter.
The central open space is the median channel; on each side is seen one of the numerous subdivisions of the lateral portions of the air-bladder. Above are the median aorta and the two lateral veins, as in fig. 3.
The facts are as follows: the Lepidostens and Amia, like many other fishes, have an air-bladder—a sac lying under the spine and above the alimentary canal, and communicating by a slit-like orifice with the upper side of the throat. With sturgeons and catfishes and most common fishes, the sac is nearly or quite simple, and the communication with the throat may be very narrow or even closed Such fishes are not known to swallow air, and there is need of further information as to the composition and source of the contained gas. But the air-bladder of Amia and Lepidosteus is divided into many cells,
